DS,
Since there may be a trend toward non-conducting waterlines, I don't regard a waterline as a primary electrode requiring #4 bare copper grounding.
But even if you don't use the water line as a grounding electrode, you still must bond the interior piping with a conductor sized per Table 256-66 because of 250-104.
I don't think there is any requirement to make the bonding connection to the interior piping near the point of entrance. That rule was put in for the connection of the grounding electrode conductor to the water pipe. The reason this connection is required within 5' of the water pipes entrance is to minimize the possiblility of the grounding electrode being disconnected by a non-metallic piping repair.
As far as knowing if the piping is metallic or not, there is not a good way to know for sure unless it is new construction. In service upgrades you can only make a guess based on area practices.
